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United States Patent |
6,091,565
|
Schwarz
,   et al.
|
July 18, 2000
|
Head assembly having a single pass servo writer
Abstract
A tape servo system includes tape having bands of tracks including at least
one data band having a plurality of data tracks of track pitch P and a
servo band dedicated for servo information. The servo band includes two or
more noncontiguous servo tracks with each pair of adjacent servo tracks of
the two or more noncontiguous servo tracks having a center to center
separation equal to M * P, wherein M for each pair of adjacent servo
tracks may be any integer .gtoreq.2. The system may further include a head
assembly having a single magnetoresistive read element tapped to provide
at least (K+1) tapped servo read elements for use in reading servo
information written to the servo band; wherein K is equal to the integer M
for the pair of adjacent servo tracks having the greatest center to center
separation and a repositioning assembly for repositioning the head
assembly as a function of the servo information. Further, the center to
center separation between pairs of adjacent servo tracks of the two or
more noncontiguous servo tracks may be different for at least two pairs of
adjacent servo tracks. A servo tracking data recording tape with two or
more noncontiguous servo tracks having center to center separation between
pairs of adjacent servo tracks being different for at least two pairs of
adjacent servo tracks is also provided along with a method for servo track
identification for use therewith. Further, track read/write head
assemblies wherein the servo read and write elements are along the same
gap lines as the data read and write assemblies, respectively, are
provided.
Inventors:
|
Schwarz; Theodore A. (Woodbury, MN);
Youngquist; Robert J. (White Bear Lake, MN);
Tran; Hung T. (Woodbury, MN)
|
Assignee:
|
Imation Corp. (Oakdale, MN)
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Appl. No.:
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322879 |
Filed:
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May 28, 1999 |
Current U.S. Class: |
360/75; 360/78.02 |
Intern'l Class: |
G11B 021/02 |
Field of Search: |
360/75,77.12,78.02,113
|
References Cited
U.S. Patent Documents
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4422111 | Dec., 1983 | Moeller et al.
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4472750 | Sep., 1984 | Klumpp et al.
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4530019 | Jul., 1985 | Penniman.
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4539607 | Sep., 1985 | Fujiki.
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4616272 | Oct., 1986 | Moriyama.
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4866548 | Sep., 1989 | Rudi.
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4975791 | Dec., 1990 | Eggebeen.
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4977472 | Dec., 1990 | Volz et al.
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4979051 | Dec., 1990 | Eggebeen.
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4996609 | Feb., 1991 | Joannou.
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5008765 | Apr., 1991 | Youngquist.
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5079663 | Jan., 1992 | Ju et al.
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5121270 | Jun., 1992 | Alcudia et al.
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5187699 | Feb., 1993 | Raaymakers et al.
| |
5196969 | Mar., 1993 | Iwamatsu et al.
| |
5210660 | May., 1993 | Hetzler.
| |
5229895 | Jul., 1993 | Schwarz et al.
| |
5262908 | Nov., 1993 | Iwamatsu et al. | 360/77.
|
5331493 | Jul., 1994 | Schwarz.
| |
5367414 | Nov., 1994 | Kelly et al.
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5377057 | Dec., 1994 | Solhjell.
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5379165 | Jan., 1995 | Pahr.
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5384671 | Jan., 1995 | Fisher.
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5394277 | Feb., 1995 | Pahr et al.
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5396376 | Mar., 1995 | Chambors et al.
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5396380 | Mar., 1995 | Shimizu et al.
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5418670 | May., 1995 | McClure et al.
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5424882 | Jun., 1995 | Kazawa.
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5426543 | Jun., 1995 | Dy et al.
| |
5432652 | Jul., 1995 | Comeaux et al. | 360/77.
|
5448430 | Sep., 1995 | Bailey et al.
| |
5450257 | Sep., 1995 | Tran et al.
| |
5452150 | Sep., 1995 | Henneberger et al.
| |
5453887 | Sep., 1995 | Negishi et al.
| |
5488525 | Jan., 1996 | Adams et al.
| |
5541793 | Jul., 1996 | Schwarz.
| |
5574602 | Nov., 1996 | Baca et al.
| |
5617269 | Apr., 1997 | Gordenker et al.
| |
5675448 | Oct., 1997 | Molstad et al.
| |
5726834 | Mar., 1998 | Ayres et al.
| |
Foreign Patent Documents |
43 16 896 | Nov., 1992 | DE.
| |
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| |
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| |
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| |
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| |
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| |
WO 94/12975 | Jun., 1994 | WO.
| |
Other References
W. McCormick, "Multielement Servoing Head," IBM Technical Disclosure
Bulletin, 17(4), pp. 979-980 (1974).
T. Schwarz, "Re-recordable Servo System for Multi-Track Tape," IBM
Technical Disclosure Bulletin, 25(2), pp. 778-779 (1982).
|
Primary Examiner: Hindi; Nabil
Attorney, Agent or Firm: Levinson; Eric D.
Parent Case Text
Divisional application of prior application Ser. No. 08/811,390, filed on
Mar. 4, 1997, now U.S. Pat. No. 5,546,158.
Claims
What is claimed is:
1. A head assembly comprising:
a plurality of data write elements along a first gap line;
a plurality of data read elements along a second gap line;
a single pass servo writer including servo write elements along the first
gap line; and
a single magnetoresistive servo read element tapped to provide a plurality
of segmented servo read elements embedded between the plurality of data
read elements along the second gap line.
2. The head assembly according to claim 1, further including a servo erase
element along a third gap line.
Description
FIELD OF THE INVENTION
The present invention relates to tape servo tracking. More particularly,
the present invention relates to tape servo systems and methods, servo
track configurations, and read/write heads utilized therewith.
BACKGROUND OF THE INVENTION
It is common to provide magnetic tape write/read head assemblies having one
or more write/read transducer heads positioned transverse to the intended
path of a magnetic recording medium, i.e., tape, for writing data on and
reading data from parallel tracks on the tape. It is also known to include
servo information on at least some of the tracks and provide servo
transducer heads for reading such information to enable control of the
lateral position of the head assembly, thereby dynamically maintaining the
respective transducer heads of the head assembly relative to tape tracks.
With the use of servo control, data track widths can be made significantly
narrower and the capacity of the recording medium can therefore be
increased.
Various techniques for providing the servo information contained in tracks,
i.e., servo tracks, have been previously employed. For example, it is
known to provide dedicated servo tracks on the medium at the time of
manufacture. However, it is desirable to enable an end-user to write a
servo pattern on the medium in the field as opposed to factory writing of
servo information. This allows the end-user to add the servo information
to either a blank medium or utilize a medium which was either
intentionally or unintentionally erased.
There are a substantial number of different servo track configurations for
providing servo control. For example, some of the different configurations
are generally characterized by the utilization of either alternating
information containing tracks embedded on an erased band and a single head
or a center tapped head, as shown in FIG. 1, or alternating tracks with
different distinguishable characteristics such as one or more discrete
monofrequencies and a single head or a center tapped head, such as shown
in FIG. 2. As shown in FIG. 1, a single servo transducer 14 is utilized
for sensing servo information on the alternating servo tracks 12 in servo
band 10 on an erased background for use in positioning data heads 19
within the data bands 18. Alternatively, a center tapped head 16 may be
utilized for providing position error signals as a function of the
position of the head 16 over the tracks 12 within the servo band 10.
As shown in FIG. 2, a single servo head 24 may be utilized for providing
servo information from alternating servo tracks 22 within servo band 20
having different distinguishable characteristics. The information is then
used to position the data heads 29 correctly within the data bands 28 for
performing read and/or write functions. Alternatively, a center tapped
head (or two servo transducer elements) 26 may be utilized to generate a
position error signal from the servo information recorded within the servo
band 20.
However, these different servo configurations have ambiguity associated
with identifying which servo track is being used for deriving the position
error signal to provide for servo control of the system. Although the
servo track provides adequate positioning information, it does not provide
any information as to which servo track the servo head is currently
utilizing to generate the position error signal for servo control.
Therefore, if the servo transducer is unintentionally repositioned, a
misidentification of the servo track being used for servo positioning of
the data read/write heads occurs.
Various configurations attaining some improvement with respect to the above
configurations are shown in FIGS. 3, 4, and 5, wherein multiple heads are
utilized for generating positioning information from the servo information
written in the servo band. As shown in FIG. 3, multiple heads 32 are
utilized for reading servo information from a servo track 34 recorded in
servo band 30 for positioning data heads 36 within the data bands 38.
Further, as shown in FIG. 4, multiple servo heads 42 are utilized for
reading servo information from a pair of distinguishable servo tracks 44
within servo band 40 to position data heads 46 within data bands 48.
The above configurations either rely on a single servo track utilizing
multiple servo heads (wherein the number of heads is at least N-2 and N is
the number of data tracks in a data band), rely on a pair of
distinguishable servo tracks which also requires the use of at least N-2
servo heads, or rely on a set of alternating distinguishable tracks which
fill the servo bands. With the use of multiple heads and a single servo
track or a pair of distinguishable servo tracks (FIGS. 3 and 4), an
undesirable large number of servo heads is necessary. With regard to the
latter multiple alternating distinguishable tracks, such tracks are very
difficult to write in situ in a tape drive.
For example, in writing multiple distinguishable tracks, servo write heads
may not be placed adjacent to one another. Therefore, when servo tracks
are written contiguous with one another as in the pair of alternating
distinguishable servo tracks (FIG. 4) and set of multiple alternating
distinguishable servo track (FIG. 2) configurations, it is required that
they be written on multiple passes or with heads along multiple gap lines.
For precision writing, this typically requires that the pattern be written
in the factory. In many cases it is desirable to write servo information
in the field. Further, although with the use of multiple alternating
distinguishable tracks written across the servo band, the number of servo
heads necessary is reduced to one or two heads, the problem of ambiguity
in servo track identification is still applicable.
In another servo configuration which utilizes multiple spaced heads as
shown in FIG. 5 (extracted from U.S. Pat. No. 5,262,908, to Iwamatsu et
al., issued Nov. 16, 1993), multiple heads 52 are utilized for reading
information from a plurality of spaced servo tracks 54 within servo band
50 for positioning data read/write heads 56 within data bands 58. However,
with respect to such a configuration and the other configurations as
described above which use multiple servo heads, it is difficult to produce
head assemblies that include such multiple servo heads. Particularly, in
thin film heads, limited space is allotted between adjacent data bands and
therefore, space is limited for the leads from each of the multiple servo
heads. In high track density heads, such leads are much larger than the
width of the track pitch. As such, production of such multiple heads in
the head assembly in such thin film heads is difficult.
For the above reasons and other reasons that will be apparent from the
description below, alternatives to the configurations such as those
described above are needed to overcome difficulties associated therewith.
For example, the unambiguous identification of individual servo tracks is
desired. Further, it is desired to reduce the number of servo heads
necessary for providing servo control and also it is desirable to write
servo tracks in the field in a single pass.
SUMMARY OF THE INVENTION
A tape servo system in accordance with the present invention includes tape
having a plurality of bands of tracks. The plurality of bands of tracks
include at least one data band having a plurality of data tracks of track
pitch P and a servo band dedicated for servo information. The servo band
includes two or more noncontiguous servo tracks with each pair of adjacent
servo tracks of the two or more noncontiguous servo tracks having a center
to center separation equal to M * P, wherein M for each pair of adjacent
servo tracks may be any integer .gtoreq.2. The system further includes a
head assembly having a single magnetoresistive read element tapped to
provide at least (K+1) tapped servo read elements for use in reading servo
information written to the servo band; wherein K is equal to the integer M
for the pair of adjacent servo tracks having the greatest center to center
separation. A repositioning assembly of the system repositions the head
assembly as a function of the servo information read from the servo band
using the servo read elements.
In one embodiment of the system, each data band includes N data tracks, the
number of servo read elements is equal to H, the number of servo tracks is
equal to S, and further S*(H-1).gtoreq.N. In another embodiment of the
system, the center to center separation between pairs of adjacent servo
tracks of the two or more noncontiguous servo tracks is different for at
least two pairs of adjacent servo tracks. In yet another embodiment of the
system, the head assembly includes a plurality of servo write elements for
identically writing the plurality of servo tracks in a single pass; the
servo write elements having the same gap line as the data write elements.
Another tape servo system in accordance with the present invention includes
tape having a plurality of bands of tracks. The plurality of bands of
tracks include at least one data band having a plurality of data tracks of
track pitch P and a servo band dedicated for servo information. The servo
band includes two or more noncontiguous servo tracks with each pair of
adjacent servo tracks of the two or more noncontiguous servo tracks having
a center to center separation equal to M * P, wherein M is any integer
.gtoreq.2. The center to center separation between pairs of adjacent servo
tracks of the two or more noncontiguous servo tracks is different for at
least two pairs of adjacent servo tracks. The system further includes a
head assembly including a plurality of servo read elements (H) for use in
reading servo information written to the servo band. The number of servo
read elements (H) is equal to at least K+1, wherein K is the number of
track pitches between the centers of the two servo tracks of a pair of
adjacent servo tracks having the greatest center to center separation. A
repositioning assembly of the system repositions the head assembly as a
function of the servo information read from the servo band using the
plurality of servo read elements.
A servo tracking data recording tape in accordance with the present
invention is also described. The tape includes at least one data band
having a plurality of data tracks of track pitch P and a servo band
dedicated for servo information. The servo band includes two or more
noncontiguous servo tracks with each pair of adjacent servo tracks of the
two or more noncontiguous servo tracks having a center to center
separation equal to M * P, wherein M is any integer .gtoreq.2. The center
to center separation between pairs of adjacent servo tracks of the two or
more noncontiguous servo tracks is different for at least two pairs of
adjacent servo tracks.
In various embodiments of the systems and tape described above, the center
to center separation between pairs of adjacent servo tracks is different
for each pair of servo tracks across the servo band. Further, the
separation between pairs of adjacent servo tracks may be different by one
or more track pitches from one pair of servo tracks to a subsequent pair
of servo tracks across the servo band, and yet further, the center to
center separation between pairs of adjacent servo tracks may monotonically
increase by one track pitch from one pair of servo tracks to a subsequent
pair of servo tracks across the servo band.
A system for writing servo track information within a servo band of a tape
in accordance with the present invention is also described. The writing
system includes tape including a plurality of bands of tracks. The
plurality of bands of tracks include at least one data band having a
plurality of data tracks of track pitch P and a servo band dedicated for
servo information. The system further includes a head assembly including a
plurality of data write elements and a servo writer having the same gap
line as the plurality of data write elements. The servo writer writes two
or more noncontiguous servo tracks in the servo band with each pair of
adjacent servo tracks of the two or more noncontiguous servo tracks having
center to center spacing equal to M * P, wherein M for each pair of
adjacent servo tracks may be any integer .gtoreq.2.
In one embodiment of the system, the head assembly further includes a servo
erase head along another gap line for erasing the servo band.
A method of servo track identification in accordance with the present
invention includes spacing a plurality of noncontiguous servo tracks such
that pairs of adjacent servo tracks have a center to center separation
therebetween that is different for at least two pairs of adjacent servo
tracks of the plurality of noncontiguous servo tracks. The method further
includes sensing whether servo read elements of at least one pair of
adjacent servo read elements are positioned proximate to the center of at
least one of the servo tracks.
In one embodiment of the method, the number of servo read elements is equal
to at least K+1, wherein K is the number of track pitches between the
centers of two servo tracks of a pair of adjacent servo tracks of the
plurality of noncontiguous servo tracks having the greatest center to
center separation. In another embodiment of the method, the method further
includes comparing the sensed information to a predetermined algebraic
code identifying each servo track.
A method of reading servo information is also described. The method
includes providing a tape including a plurality of bands of tracks. The
plurality of bands of tracks include at least one data band having a
plurality of data tracks of track pitch P and a servo band dedicated for
servo information. The servo band includes two or more noncontiguous servo
tracks with each pair of adjacent servo tracks of the two or more
noncontiguous servo tracks having a center to center spacing equal to M*P,
wherein M for each pair of adjacent servo tracks may be any integer
.gtoreq.2. A tapped single magnetoresistive read element is positioned
proximate the tape to provide K+1 tapped servo read element signals
representative of K+1 servo read elements, wherein K is equal to an
integer M of the pair of adjacent servo tracks having the greatest center
to center separation. The method further includes cycling selectively
through the K+1 tapped servo read element signals representative of the
tapped servo read elements to provide a pair of outputs representative of
the position of adjacent servo read elements of the tapped servo read
elements relative to one or more of the noncontiguous servo tracks and
comparing the pair of outputs to determine a position error signal as a
function thereof.
A head assembly in accordance with the present invention includes a
plurality of data write elements along a first gap line, a plurality of
data read elements along a second gap line, a single pass servo writer
including servo write elements along the first gap line, and a single
magnetoresistive servo read element tapped to provide a plurality of
segmented servo read elements embedded between the plurality of data read
elements along the second gap line.
In one embodiment of the head assembly, the assembly further includes a
servo erase element along a third gap line.
Other head assemblies are also described including a head assembly having a
plurality of data write elements along a write gap line and a single pass
servo writer including servo write elements along the write gap line for
writing two or more noncontiguous servo tracks. Yet another head assembly
includes a single magnetoresistive read element and leads for tapping the
single magnetoresistive read element at a spacing equal to a data track
pitch with which the head assembly is utilized to provide at least three
segmented servo read elements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1-5 are various prior art servo system configurations. FIG. 1 is a
configuration including alternating servo tracks on an erased background.
FIG. 2 is a servo configuration including alternating servo tracks with
different distinguishable signal characteristics. FIG. 3 is a servo
configuration including a single servo track utilizing multiple servo
heads. FIG. 4 is a pair of distinguishable servo tracks with the use of
multiple servo heads. FIG. 5 is a servo configuration including multiple
spaced servo tracks and multiple servo heads.
FIG. 6 is a schematic illustration of a tape servo system in accordance
with the present invention.
FIG. 7 is a more detailed view of the tape of FIG. 6 in accordance with the
present invention.
FIG. 8A is a detailed illustration of the servo band and a portion of the
data bands as shown in FIG. 7.
FIG. 8B is a detailed illustration of an alternate configuration of the
servo band and a portion of the data bands as shown in FIG. 7.
FIG. 9 is a read layer of a head assembly having a centralized servo read
section embedded in data read elements.
FIG. 10A is a detailed view of one portion of the servo read section as
shown in FIG. 9.
FIG. 10B is a detailed view of an alternate configuration of the servo read
section as shown in FIG. 9.
FIG. 11 is a write layer of a head assembly including a servo writer
embedded in the data write elements of the head assembly.
FIG. 12 is a more detailed illustration of the servo writer and a pair of
adjacent data write elements as shown in FIG. 11.
FIG. 13 is a block diagram of servo read circuitry of FIG. 1 in accordance
with the present invention.
FIG. 14 is an alternate servo read element and servo track configuration in
accordance with the present invention.
FIG. 15 is a more detailed view of the alternate servo read element and
servo track configuration as shown in FIG. 14.
FIG. 16 is a further configuration showing the spacing of servo tracks as
the number of servo tracks in the configuration of FIG. 14 is increased.
DETAILED DESCRIPTION OF THE EMBODIMENTS
FIG. 6 schematically illustrates a closed loop tape servo system 60 for use
in reading and writing to magnetic tape 64. The tape servo system 60
includes a head assembly 62 positionable transversely relative to the
length of tape 64 by positioning actuator 68. Servo information recorded
in a servo band 76 of tape 64 is accessed utilizing head assembly 62 which
includes a single tapped magnetoresistive read element 80 and multiple
data read elements 82 along a common gap line 166, multiple servo write
elements 102 and multiple data write elements 104 along a second common
gap line 167, and a servo erase element 190 along a third gap line 168.
The head assembly 62, is capable of writing servo track configurations in
accordance with the present invention in a single pass. Further, the head
assembly 62 provides signals representative of the position of the tapped
servo read elements of the single tapped magnetoresistive read elements 80
relative to servo tracks in servo band 76 to servo read circuitry 63 of
position error signal generating circuitry 70. Servo read circuitry 63
generates outputs representative of servo information in the servo band
for use by processing unit or control logic 65 which generates a position
error signal command based on the servo information from the servo read
circuitry 63.
The head assembly 62 is then positioned by positioning actuator 68 in
response to a position error signal command conditioned by conditioning
circuitry 67, such as an amplifier, to move the head assembly 62 such that
alignment of the tapped servo read elements of the single magnetoresistive
element 80 and servo tracks in the servo band 76 is achieved. Thereby,
positioning of data read elements 82 and/or data write elements 104 are
correctly positioned for reading and writing data to data tracks of
individual data bands within the groups of data bands 72 of tape 64.
Generally, the servo system 60 can employ servo write elements and servo
read elements in the same gap lines as the data write and read elements,
respectively. However, various concepts in accordance with the present
invention are equally applicable to the use of multiple elements provided
along separate gap lines, multiple elements provided by multiple spaced
read elements as opposed to a tapped single magnetoresistive element, head
assemblies including only servo read elements without servo write elements
(i.e., the servo information written at the factory), head assemblies not
including a servo erase element (i.e., field servo writing only possible
on a pre-erased servo band), and various other head assemblies as would be
readily apparent to one skilled in the art.
As is described further below with reference to the alternate servo track
configurations of FIGS. 14-16, the present invention contemplates the use
of unique patterns of noncontiguous identical, i.e., monofrequency, servo
tracks written on an erased servo band of the tape 64. More particularly,
the unique patterns are provided with multiple spacing arrangements
between the servo tracks. The unique patterns are selected in order to
minimize servo track identification ambiguity and to minimize the number
of servo read elements required to achieve servo control.
As shown in FIG. 7, the tape 64 is divided into an integral number of
groups of bands of tracks including groups of data bands 72. Within each
group of data bands 72, each of the tracks is dedicated to a specific
individual data band such as data band 74. One of the bands of tape 64,
typically the center band, is dedicated for servo information and is shown
in FIG. 7 as servo band 76. The servo band 76 is centered between the
groups of data bands 72. However, it is not necessary for the servo band
76 to be centered between the data bands as it could be positioned towards
one edge of the tape or the other edge of the tape, or further could be
positioned at one tape edge or the other tape edge. However, preferably
the servo band 76 is centered to decrease tracking tolerances resulting
from tape related track displacement due to, for example, tape contraction
or expansion resulting from environmental change or ageing. The center
positioning decreases the distance between the servo read elements 80 and
the furthest most data elements 83 (FIG. 7). In each of the individual
data bands 74, the data tracks are contiguous, e.g., the data tracks are
directly adjacent one another.
As shown in the more detailed view of the servo band 76 in FIG. 8A, servo
band 76 includes two or more noncontiguous servo tracks, e.g.,
noncontiguous servo tracks being servo tracks which are physically
separated by more than one-half track pitch P, in other words, are not
directly adjacent to one another. Generally, in accordance with the
present invention, the tape 64 includes a predetermined number of
individual data bands 74 having a particular number of data tracks therein
of track pitch P. Further, the tape 64 includes servo band 76 dedicated
for the servo information with the servo band 76 including two or more
noncontiguous servo tracks 78, such as identically written servo tracks
85, 87, and 89. The center to center spacing between adjacent servo
tracks, such as, for example, servo track 85 and servo track 87 as shown
in FIG. 8A, is equal to M * P, wherein M may be any integer greater than
or equal to 2. In the present invention, each servo track has a width that
is equal to about the track pitch P. Preferably, the width is slightly
greater than P, for example, 1.1 P or less. As such, the width of the
servo tracks need not be equivalent to the track pitch P.
The head assembly 62 of servo system 60 for use in reading the servo
information from the servo band 76 includes multiple servo read elements
which can be configured as a single magnetoresistive element tapped at the
data track pitch, as shall be described in further detail below. In
general, with S being the number of servo tracks, N being the number of
data tracks in an individual data band 74, H being the minimum number of
servo read elements 80 necessary for reading the servo tracks 78 in
accordance with the present invention, then the relationship between the
number of servo tracks in the servo band 76 and the minimum number of
servo read elements 80 is given by: S * (H-1)N. The minimum number (H) of
servo read elements 80 in accordance with the present invention is equal
to K+1, wherein K is equal to the integer M with M being the number of
data track pitches between the centers of a pair of adjacent servo tracks,
such as servo tracks 85 and 87 or tracks 87 and 89 (FIG. 8A).
In the illustrative embodiment of the servo track and servo read element
configuration, FIG. 8A shows the utilization of three noncontiguous servo
tracks 85, 87, and 89. Each pair of servo tracks is separated by six data
track pitches. For example, servo track pair 85 and 87 is separated center
to center by six data track pitches and servo track pair 87 and 89 is
separated center to center by six data track pitches. The configuration
shown in FIG. 8A contains eighteen data tracks in an individual data band
74 and therefore, in this particular illustrative embodiment, N=18, S=3,
M=6, and H= at least 7. It should be readily apparent to one skilled in
the art that such numbers may vary, including the number of data bands
which could be either larger or smaller as generally shown by the above
general equation. Further, although the servo band 76 is shown to be at
the center of the groups of data bands 72 for minimizing the distance
between the furthermost data head and the servo tracks, the position of
the servo band 76 may vary as previously described. Further, the tape 64
in this embodiment is generally known in the industry as quarter inch
tape, however, the present invention is applicable to other available size
tapes, such as 8 mm or 12.7 mm tape, or any other tape as would be
generally known by those skilled in the art.
FIG. 8A shows multiple servo read elements 80 in six different positions
with respect to the tape 64. The six different positions are shown in a
lateral direction for clarity even though head assembly 62 including the
multiple servo read elements 80 are moved in a direction transverse to the
length of tape 64 by positioning actuator 68. In the first position (left
to right in FIG. 8), the two servo read elements at one end of the
multiple servo read elements 80 access the center of the servo track 85
and data element 82 accesses the first data track adjacent to the servo
band 76. Likewise, in subsequent positions of the multiple servo read
elements 80, various pairs of adjacent servo read elements of the multiple
servo read elements 80 are positioned with respect to one of the
noncontiguous servo tracks 85, 87, or 89 in order to position the data
read element 82 to access the data tracks of the individual data bands 74.
It is readily apparent that the data read element 82 may be either a read
or write element depending upon the function to be provided by the drive
and is not to be taken as limiting to the present invention.
The servo tracks 78 are spaced such that each of the servo tracks 85, 87,
and 89 provide for access of six different data tracks within the
individual data band 74. As illustrated, servo read elements 80 utilize
servo track 85 to access the first six data tracks adjacent to the servo
band 76, servo track 87 is utilized to access the second six data tracks,
and servo track 89 is utilized to access the last six data tracks of the
individual data band 74. The servo tracks 78 are further separated from
the data bands by servo guard band 84 to prevent the misinterpretation of
information in adjacent individual data bands 74 as servo information.
The method of reading and writing data on tape 64 in accordance with the
present invention includes moving head assembly 62 in a direction
transverse to the length of tape 64 to access one of the dedicated servo
tracks 85, 87, 89 and thus the data track desired. The multiple servo read
elements 80 are utilized to read the servo information identically written
to the dedicated servo band to which the servo read elements 80 are
proximate. The tape servo system 60 uses this servo information to
determine the error between the position of head assembly 62 and the
desired center position on one of the servo tracks 78. The position error
information is then used to accurately position head assembly 62 utilizing
positioning actuator 68. Therefore, data read/write elements are
accurately positioned on the desired data tracks of the individual data
bands 74 to which data can be written or from which data can be read. In
general, data is written or read from the data tracks on tape 64 by moving
head 62 approximately to the position where a pair of adjacent servo read
elements of servo read elements 80 are positioned on the center of one of
the servo tracks 78. With the utilization of adjacent servo read elements
to sense the center location of the servo tracks, the width of the servo
track can vary and the tolerances for the servo track dimensions can be
loosened. This allows for such servo tracks to be more easily written in
the field as opposed to higher tolerance writing of the servo tracks in
the factory.
By spacing the centers of the servo tracks 78 multiple track pitches apart,
ambiguity of track location is reduced. In other words, the separation
between the servo tracks 78 is of a distance great enough such that if the
head slips off track by one or more tracks, such track slipping is
acknowledged. As illustrated in the various positions of the servo read
elements 80, only one pair of adjacent servo elements is allowed to access
one of the servo tracks 78. In other words, the servo read elements 80
become completely disengaged from one servo track, such as servo track 85,
without picking up any adjacent signals from adjacent servo tracks, such
as servo tracks 87 and 89.
Further, with the use of noncontiguous servo tracks, the advantage of
writing to the servo tracks on a single pass with a common servo writer,
as further described below, can be utilized. In addition, the number of
servo read elements is reduced or the number of taps of a single
magnetoresistive element is reduced with the use of multiple servo tracks.
Preferably, the servo tracks 78 are identically written such that they can
be written in the field with a single pass. However, the present invention
contemplates using different but similar densities to servo write each of
the servo tracks in the servo band, such that track identification can be
unambiguously determined. However, writing different densities would
require such servo writing to be performed in a factory and not in situ,
as there is insufficient room for three separate servo writers for writing
the plurality of densities while still having the same gap line as the
data write elements as further described below.
One alternative to using different densities in order to unambiguously
determine track identification is to use the same density on all tracks
but use varied physical separation to determine which servo track is being
accessed. Such variable physical separation to unambiguously determine
track identification is further described below with reference to FIGS.
14-16.
An alternate configuration of the servo band and adjacent individual data
bands is shown in and shall be described with reference to FIG. 8B.
Additional dimensional characteristics in the separation of the servo
tracks and data elements can be utilized such that guard bands or gaps 386
can be used between multiple data tracks within the individual data track
bands 374 along with the servo guard bands 384. Such use of gaps 386
improves the tolerance to variations in servo track placement on the tape,
i.e., such as, for example, variations that may occur due to tolerances of
the write elements used to write the servo tracks. Further, the use of
such gaps provides a band-edge guard band wherein alternate data bands can
be written in opposite directions of tape motion without encountering
additional tracking error, related to direction, between adjacent data
tracks within the same data band.
As shown in FIG. 8B, the two outer servo tracks 385 and 389 have an
additional separation from the center of servo track 387 of dP1 which is
less than or equal to the data track pitch P. Therefore, the center to
center separation of adjacent servo tracks is equal to (dP1+M*P), wherein
M is the integer number of data track pitches between the centers of the
adjacent servo tracks. The value dP1 is also the width of guard band or
gap 386 and the number of gaps or guard bands 386 in the individual data
bands 374 are equal to S-1, for example, S-1=2 in FIG. 8B. Further, the
separation from the center line of the group of servo read elements 380 to
the centerline of the adjacent data head 382 is
[G+(S-1)*(M*P+dP1)+P*(H/2)] wherein G is the width of the servo guard band
384. For example, as shown in FIG. 8B, where three servo tracks are used,
the center to center separation from center servo track 387 to the outer
servo track 385 is (6 P+dP1), i.e., M equal to six. Further, the
separation from the center line of the group of servo read elements 380 to
the center of the adjacent data element 382 is G+(15*P)+(2*dP1). In
addition, guard band 384 is provided such that if the servo read elements
380 move into the guard band region while active, a signal is not be
picked up from the adjacent data bands.
The multiple servo read elements 80 (FIG. 8A) of the head assembly 62 are
preferably provided by a tapped single magnetoresistive element. However,
multiple magnetoresistive elements may also be utilized in various
configurations of the present invention. The single magnetoresistive
element is tapped at the data track pitch across the single element as
will be described further below with respect to several embodiments
thereof.
One layer of an illustrative embodiment of a read head structure in
accordance with the present invention is shown in FIG. 9. The read layer
90 of the head assembly 62 includes two groups of data read elements 92
and a centralized seven element servo read section 94. As shown, the servo
read section 94 includes leads 98 extending from a servo read element end
portion 96 and terminating in termination pads 95. The leads of the data
elements are shown in a folded configuration wherein one lead is folded
over the other lead to reduce the space necessary for accommodating the
leads. However, any lead structure is contemplated in accordance with the
present invention and the present invention is in no manner limited by
this configuration of the data elements and leads.
The servo read element end portion 96 is shown in further detail in the
alternative embodiments of FIGS. 10A and 10B. As shown in the illustration
of FIG. 10A, the servo read element end portion 96 includes a single
magnetoresistive element 116 which is tapped at the data track pitch by
termination leads extending therefrom. As shown in FIG. 10A, such
termination leads include termination tap leads 111 and input and output
leads 110 and 112. The input and output leads, 110, 112 are utilized for
connection to a bias voltage or current source and ground for biasing the
elements. Between the outer leads 110 and 112 are six tap leads 111
positioned at the data track pitch and insulated therebetween by an
insulating material 113. The single magnetoresistive element 116 is tapped
so as to provide signals representative of seven servo read element
segments as required for use in the illustrative embodiment described with
reference to FIG. 8A. It should be readily apparent that any number of
tapped elements may be provided as determined by the desired servo
configuration utilized.
As shown in the alternate configuration of FIG. 10B, servo read end portion
296 includes single magnetoresistive element 216 and further includes
input and output segments 217, 219 fabricated of lead structure material.
The input and output segment 217, 219 are aligned with the single
magnetoresistive read element 216 to control the current flow through the
single magnetoresistive material of the single read element. As such,
current flows in a substantially linear fashion from the input lead
segment 217 to the output lead segment 219 as opposed to the embodiment of
FIG. 10A wherein current does not enter the single magnetoresistive
element 116 in a linear fashion but rather at somewhat of an angle. By
using the input and output lead segments of FIG. 10B, the current flows
more uniformly from input to output and voltages provided by the tapped
segments of the single element are more uniform when exposed to the same
conditions. The end portion 296 also includes insulating layers 213
isolating the leads 291, 210 and 212.
Further, by having the servo read element segments contiguously adjacent to
each other, adjacent segments operate as one half of a center tapped head.
Such a configuration minimizes variation in the sensitivity between two
distinct read elements due to fabrication tolerances. Further, such a
tapped configuration allows for the minimization of signal amplitude
variations due to variations in the head to tape placement. With both the
configurations of FIGS. 10A and 10B, current flow through the termination
leads 111, 291, respectively, is inhibited.
The tapped single magnetoresistive element 116 provides outputs
representative of the tapped element segments of the single element 116 to
servo read circuitry 63. The servo read circuitry 63 of the tape servo
system 60 for terminating or receiving outputs from the multiple servo
read element segments is illustrated in FIG. 13. The servo read circuitry
63 includes two banks 122, 124 of thin film amplifiers 128, 130,
respectively. The outputs of the banks of amplifiers are connected to
multiplexors 126 and 128 of the respective banks 122, 124. The amplifiers
128 and 130 are utilized to provide selectable outputs via the
multiplexors 126 and 128 from each tapped servo read element segment of
the single magneto resistive element 116. By multiplexing the individual
outputs and providing outputs from each of the banks 122, 124
representative of adjacent servo read element segments, an error signal is
generated by a comparison of the two outputs by differential amplifier
142.
The difference signal from the amplifier 142 is provided to signal
processing unit 65 (FIG. 6), such as a digital signal processor, to
provide for generation of a position error signal command to control
positioning actuator 68 for movement of head assembly 62 transverse to the
length of tape 64 for aligning the adjacent servo read element segments
with the center of the servo track. The outputs are also summed by a
summing amplifier 140 which may be utilized for providing automatic gain
control. Further, a comparator 144 may be used for comparing one of the
outputs to a reference or threshold to determine the transverse direction
the head assembly 62 is moving relative to the tape 64.
As shown in FIG. 13, one edge of tapped servo read element segment 116A is
connected to amplifier 128A of bank 122. The other edge of tapped servo
read element segment 116A, which is also at the edge of segment 116B, is
also connected to amplifier 128A and, in addition, to amplifier 130B of
bank 124. The other edge of tapped servo read element segment 116B is
connected to one input of amplifier 128C of bank 122 and further connected
to the other input of amplifier 130B of bank 124. The other tapped servo
read element segments 116C-116G are connected in a similar fashion to
respective amplifiers of the two banks 122, 124. It should be noted that
the leads of each of the servo read element segments, except for the two
outer tapped servo read element segments 116A and 116G, are each connected
to an amplifier of each bank 122 and 124 such that signals representative
of adjacent tapped servo read element segments 116 are provided to an
amplifier in opposing banks. For example, signals representative of
adjacent segments 116A and 116B are provided to bank 122 and bank 124,
respectively. As such the outputs of the respective banks 122, 124 are
representative when selected by the respective multiplexors of adjacent
servo read element segments. The outputs can then be compared to provide a
position error signal with respect to the position of a pair of adjacent
servo read element segments relative to the center of a servo track.
The operation of the servo system 60 shall now be described with reference
to the tapped servo read element 116, representing the multiple servo read
elements 80, being moved across the servo band shown in FIG. 8. As the
head assembly 62 is moved transversely with respect to the length of tape
64, servo read element segments 116A and 116B are moved across the first
servo track 85. As servo element 116A is moved over the servo track 85,
the signal upon preamplifier 128A is increased. With only servo read
element 116A positioned on servo track 85, the difference value generated
by differential amplifier 142 is representative of the fact that only
servo read element 116A is positioned over servo track 85. As servo read
element 116B begins to move over the servo track 85 and a portion of servo
read element 116A is moved off of servo track 85, the selected outputs
from the bank 122 and bank 124 representative of the adjacent segments
116A and 116B get closer to being the same. The outputs of multiplexor 126
and 128 are filtered and rectified by filters 128, 136 and rectifiers 134,
138 and provided to differential amplifier 142. The differential amplifier
142 compares the outputs, and as the difference between the two outputs
approaches zero, the signal processing unit 65 determines that the servo
track center has been found by the differential pair of sensors, i.e., the
tapped servo read elements segments 116A and 116B. Therefore, the head
assembly 62 achieves servo lock on servo track 85. Thereafter, data
read/write element 82 can then be utilized to read or write data to or
from the first track adjacent the servo band 76. It should be noted that
the number of data elements for reading and writing are numerous as shown
in FIG. 7 and the head assembly of FIG. 6.
Not shown in FIG. 13 is an AC coupling capacitor or a compensation circuit
in the preamplifiers required to manage the large voltage drop across each
servo read element segment relative to the signal provided to the
preamplifiers. For example, the signal of the tapped servo read element
segment may be typically, for example, 1 to 3 percent of the DC voltage
across the entire single magnetoresistive element.
It should be readily apparent that the concept of odd/even banks of
amplifiers selectable to provide outputs for difference comparison
utilizing tapped servo read elements may include any number of servo read
element segments and any number of amplifiers depending upon the servo
configuration utilized. The illustrative embodiment of FIG. 13 provides
for the termination of the seven servo read element segments as utilized
in conjunction with the servo configuration shown in FIG. 8A and 8B.
However, the present invention is in no manner limited to this particular
illustrative embodiment, but is limited only as described in the
accompanying claims.
Although the servo tracks of the various configurations may be written at
the factory, it is preferable that the head assembly 62 include a servo
writer 102 for writing the servo tracks in the field, i.e., in situ. Servo
writer 102 in accordance with the present invention as shown in the
illustrative drawing of the head assembly 62 in FIG. 6, is embedded in the
data write elements 104 as shown in FIG. 11 along a common gap line 167
(FIG. 6). FIG. 11 is an illustration of a data write layer 100 of the head
assembly which shows multiple data write elements 104 with the servo
writer 102 centered between two groups of the data write elements 104. The
servo writer 102 is offset 1/2 of the data track pitch from the data write
elements such that the servo tracks are positioned for the servo read
elements to read and properly align the data elements on the data tracks
when centered.
The head assembly 62 is a thin film head and the servo writer 102 includes
a thin film servo write comb structure 106, shown in further detail in
FIG. 12 along with further detail of two adjacent data write elements 104.
The servo writer further includes termination leads 108 extending
therefrom.
As shown in FIG. 12, the comb structure 106 is for use in writing
noncontiguous servo tracks in a single pass of the tape 64. The servo
writer 102 is positioned in the center of the data elements 104 to
minimize the separation of the outermost data elements from the servo band
76, although other positions of the servo band may be utilized. The data
write elements 104 are uniformly separated by an integer number of data
track pitches unless guard bands are utilized as shown in FIG. 8B.
The thin film servo writer 102 includes a common bottom pole 166, a
continuous set of coils arranged in one or more layers 168, and a top pole
172 with two or more teeth or fingers separated for writing the servo
tracks as desired for the various servo configurations described herein. A
back closure 170 to the bottom pole 166 is also provided. Further, as
shown in FIG. 12, the top pole 172 is recessed from the tape bearing
surface by several microns to prevent recording in the region between the
teeth where writing of servo information is undesired. With a common coil
for the various teeth, identical servo tracks are written. As the servo
tracks are written at the same time and each of the teeth have a common
gap line, parallelism, and/or collinear transition, between the tracks is
easily maintained.
The comb structure, as shown in FIG. 12, reflects a three finger or tooth
comb such as utilized in writing the servo tracks as illustrated in FIG.
8A. The servo writer 102 occupies approximately the width of an individual
data band 74. Further, the teeth of the comb-like structure 106 forming
the individual write poles have a common planar gap line 167 (FIG. 6)
which is the same as the data write elements 104. In an initial pass of
the tape 64 across the head assembly 62, the servo information can be
written to a pre-erased servo band. Typically, this is only performed
once. Subsequently, all data writes or reads are made while the head
assembly 62 is being servo controlled. This obviates the need for factory
servo writing capability. If the servo information is inadvertently
damaged, it can be rewritten by the drive using the servo writer 102.
The servo writer 102 is embedded between the data write elements with the
use of common thin film processing steps. For example, with formation of
the servo writer, common processing steps for forming both the top poles
of the servo writer 102 and the top poles of the data write elements 104
are used. The steps of the thin film process for forming both types of
write elements are common between the servo writer and the data write
elements allowing the elements to share a common gap line. For example,
typical common wafer level simultaneous construction of data and servo
write elements includes depositing on an appropriate ceramic substrate
such as alumina titanium-carbide (Al.sub.2 O.sub.3 TiC) the first or
bottom pole layer of high-moment, low coercivity magnetic material, such
as permalloy, NiFe, or cobalt zirconium tantalum (CZT). An insulating, gap
forming layer of alumina (Al.sub.2 O.sub.3) is then deposited. Using
photolithography techniques, one or more layers of coils, displaced from
where the front gap will be formed by lapping, are plated with the
requisite insulation layers of baked photoresist. A top smoothing layer of
baked photoresist above the coils is deposited and a layer of the same
magnetic material used for the first magnetic layer is deposited thereon
to form the top pole. A thick layer of alumina, sufficiently thick to
allow lapping of the film side of the substrate to form a planar surface,
is deposited and the film side of the wafer is lapped to achieve a planar
surface.
Likewise, the servo read elements can be embedded in the data read elements
with the use of common thin film processing steps. The steps of the thin
film process for forming both types of read elements are common between
the servo read elements and the data read elements allowing for common
formation and common gap lines for the servo read elements and data read
elements as shown in FIG. 9. For example, typical common wafer level
simultaneous construction of data or servo read elements includes
depositing on an appropriate ceramic substrate, such as alumina
titanium-carbide (Al.sub.2 O.sub.3 TiC), a first shield layer of high
permeability, low coercivity magnetic material, such as permalloy, NiFe,
or cobalt zirconium tantalum (CZT). An insulating, gap forming layer of
alumina (Al.sub.2 O.sub.3) is then deposited. Using photolithography
techniques, a patterned magnetoresistive read sensor sandwich consisting
of very thin films of permalloy and magnetic and non-magnetic layers is
deposited. A second alumina layer is then deposited and a layer of the
same magnetic material used for the first magnetic layer is deposited
thereon to form the top shield. Thereafter, a thick protective layer of
alumina is deposited and lapped to a planar surface.
Although increased servo track spacing reduces the ambiguity in
identification of servo tracks and thus reduces the likelihood of
misidentification due to a head slipping off track by one or more servo
tracks, some ambiguity may still exist. Ambiguity of servo track
identification can be eliminated by using identically written servo tracks
but using different varied physical separations between the servo tracks
to determine which servo track is being accessed. Such physical separation
to unambiguously determine servo track identification is described below
with reference to the alternate servo configurations shown in FIGS. 14-16.
By providing variable spacing between pairs of servo tracks which can be
written identically and simultaneously, each servo track can be uniquely
identified utilizing contiguously configured servo read elements even
though none of the servo tracks have distinguishing characteristics, i.e.,
such as, for example, varied frequency, density.
Positive track identification with use of a single pass servo writer can be
achieved by coding the layout of the servo tracks, i.e., to provide
differentiated spacing between two or more servo track pairs or each servo
track pair. One form of this is to increase the spacing one track pitch
between each subsequent pair of servo tracks as described further below
which can be written with a servo writer similar to that of FIG. 12 with
spacing differentials between the teeth of the writer.
A variable spaced servo track configuration using the differentiated
spacing set forth above is shown in FIG. 14. The servo system
configuration includes data bands 202 with a servo band 200 positioned at
the center therebetween. The servo band 200 includes servo tracks 204 and
multiple servo read elements 206. In accordance with the present
invention, the center to center spacing between servo tracks of the
adjacent servo track pair 210, 212 is about two data track pitches, and
the center to center spacing between servo tracks of the servo track pair
212, 214 is about three data track pitches.
The guard bands 208 separate the coded servo tracks 204 from the data bands
202 to allow the signal from the data band to be sufficiently reduced so
as not to be interpreted as a servo signal accessible by the servo read
elements. However, guard bands on the edges of the servo band 200 are
typically not required if the servo tracks are written simultaneously and
identically with the same monofrequency which is substantially different
from the data frequencies.
The servo track configuration as shown in FIG. 14 is shown in further
detail in FIG. 15 minus the guard bands 208. Adjacent to the servo band
200 and various positions of servo read elements 206, as shown in FIG. 14,
is an algebraic code which illustrates the uniqueness of each position of
the servo read elements 206 with respect to the differentially spaced
servo tracks 204. As shown in FIG. 15, a monotonically increasing
separation between servo tracks of pairs of adjacent servo tracks by an
additional track from one servo track pair to a subsequent pair of servo
tracks is shown. However, other codes may also be used. For example, the
code could be a binary code of spacings of 1, 2, 4, 8 . . . between
subsequent pairs of tracks or the pairs of adjacent servo tracks may be
spaced at random. Further, multiples of the track pitch interval spacing
may also be utilized.
In operation, as illustrated in FIG. 15, servo read elements C and D are
moved to a position whereat signals are received by servo read circuitry
from servo read elements. The servo read circuitry may be similar to servo
read circuitry 63, but any circuitry which can sense the position of
adjacent servo read elements relative to the servo tracks may be utilized.
The signals representative of each the multiple servo elements 206 may be
multiplexed or cycled through to determine the adjacent servo read
elements that are positioned adjacent a servo track. After adjacent servo
read elements have locked on a particular servo track, such as elements C
and D locking on the center of servo track 210, the outputs representative
of each of the multiple servo read elements are cycled through to identify
which servo track the elements C and D have locked on. For example, when
the servo elements C and D have locked on servo track 210, the outputs of
the multiple servo elements correspond to the code ABCD. The outputs are
provided to a drive processing unit with which the head assembly 62 is
utilized. In this manner, it is determined by the drive processing unit
that the adjacent servo read elements C and D are locked onto servo track
210. As similarly described previously with respect to the operation of
the tapped servo read elements with reference to FIG. 8A, when elements C
and D are positioned such that the signals therefrom are equal, the center
of servo track 210 is detected and servo lock is achieved. Reading and
writing functions may then be performed.
As the servo read elements 206 are moved proximate the other servo tracks
212 and 214, unique codes also identify which servo tracks the elements
are locked onto. For example, in the last position shown, elements A and B
are adjacent servo track 214 and the unique code ABCD are used to identify
servo track 214. As such, in each position of the servo elements A, B, C,
and D, a different code is available so as to unambiguously identify the
servo track to which the pair of adjacent servo elements are locked.
FIGS. 16 illustrates the progression for the next set of increased data
tracks per servo band. For example, if a number of data tracks in a data
band is 10, then the number of servo tracks 222 in servo band 220 is four
with a center to center separation between the furthest apart servo bands
being four data track pitches as shown in FIG. 16. As such, fourteen
algebraic codes are available for illustrating the unique position of six
servo read elements with respect to the servo tracks 222.
In general, the number of servo read elements for use in the variably
spaced servo track configurations is equal to at least K+1, wherein K is
equal to the number of track pitches between the centers of the servo
tracks for the pair of adjacent servo tracks which are farthest apart. For
example, as shown in FIG. 15, the number of track pitches between the
centers of the servo tracks 212 and 214 is three. Therefore, the number of
servo read elements 206 required is at least four. Likewise, with the
center to center spacing between the pair of servo tracks farthest apart
being four track pitches, the minimum number of servo read elements is at
least five. However, as shown in FIG. 16, in order to provide unique codes
for each of the possible servo read element positions in the servo band to
service individual data bands of 10 data tracks, at least 6 servo read
elements are necessary.
It should be readily apparent that the various elements as described with
respect to the present invention may be utilized separately, together in a
system, or with other servo configurations, and the present invention is
limited only in accordance with the accompanying claims. For example, the
differentially spaced servo track configurations as described with respect
to FIGS. 14-16 may be utilized with servo read elements that are formed
from a tapped single magnetoresistive element or may further include a
servo read element configuration wherein such elements are not tapped, but
rather separate heads are used. Further, for example, the servo writer
which may be utilized to form a single pass to write the noncontiguous
servo tracks at a mono-frequency as described herein need not be a part of
the head assembly. Such servo tracks may be written in the factory as
opposed to being written in situ. Likewise, the servo read circuitry, as
previously described, may be utilized in conjunction with the variably
spaced servo track configurations described with respect to FIGS. 14-16
with modifications as would be known to one skilled in the art.
Although the present invention has been described with reference to
particular embodiments, one skilled in the art will recognize that changes
and modifications may be made in form and detail therewith without
departing from the scope of the invention as described in the accompanying
claims.
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